Work with Protected Categorical Arrays

Open Live Script

This example shows how to work with a categorical array with protected categories.

When you create a categorical array with thecategoricalfunction, you have the option of specifying whether or not the categories are protected. Ordinal categorical arrays always have protected categories, but you also can create a nonordinal categorical array that is protected using the'Protected',truename-value pair argument.

When you assign values that are not in the array's list of categories, the array updates automatically so that its list of categories includes the new values. Similarly, you can combine (nonordinal) categorical arrays that have different categories. The categories in the result include the categories from both arrays.

When you assign new values to aprotectedcategorical array, the values must belong to one of the existing categories. Similarly, you can only combine protected arrays that have the same categories.

If you want to combine two nonordinal categorical arrays that have protected categories, they must have the same categories, but the order does not matter. The resulting categorical array uses the category order from the first array.
If you want to combine two ordinal categorical array (that always have protected categories), they must have the same categories, including their order.

To add new categories to the array, you must use the functionaddcats.

Create Ordinal Categorical Array

Create a categorical array containing the sizes of 10 objects. Use the namessmall,medium, andlargefor the values'S','M', and'L'.

A = categorical({'M';'L';'S';'S';'M';'L';'M';'L';'M';'S'},...{'S','M','L'},{'small','medium','large'},'Ordinal',真正的)

A =10x1 categorical arraymedium large small small medium large medium large medium small

Ais a 10-by-1 categorical array.

Display the categories ofA.

categories(A)

ans =3x1 cell array{'small' } {'medium'} {'large' }

Verify That Categories Are Protected

When you create an ordinal categorical array, the categories are always protected.

Use theisprotectedfunction to verify that the categories of A are protected.

tf = isprotected(A)

tf =logical1

The categories ofAare protected.

Assign Value in New Category

If you try to assign a new value that does not belong to one of the existing categories, then MATLAB® returns an error. For example, you cannot assign the value'xlarge'to the categorical array, as in the expressionA(2) = 'xlarge', becausexlargeis not a category ofA. Instead, MATLAB® returns the error:

Error using categorical/subsasgn (line 68)

Cannot add a new category 'xlarge' to this categorical array

because its categories are protected. Use ADDCATS to

add the new category.

To add a new category forxlarge, use theaddcatsfunction. SinceAis ordinal you must specify the order for the new category.

A = addcats(A,'xlarge','After','large');

Now, assign a value for'xlarge', since it has an existing category.

A(2) ='xlarge'

A =10x1 categorical arraymedium xlarge small small medium large medium large medium small

Ais now a 10-by-1 categorical array with four categories, such thatsmall < medium < large < xlarge.

Combine Two Ordinal Categorical Arrays

Create another ordinal categorical array,B, containing the sizes of five items.

B = categorical([2;1;1;2;2],1:2,{'xsmall','small'},'Ordinal',真正的)

B =5x1 categorical arraysmall xsmall xsmall small small

Bis a 5-by-1 categorical array with two categories such thatxsmall < small.

To combine two ordinal categorical arrays (which always have protected categories), they must have the same categories and the categories must be in the same order.

Add the category'xsmall'toAbefore the category'small'.

A = addcats(A,'xsmall','Before','small'); categories(A)

ans =5x1 cell array{'xsmall'} {'small' } {'medium'} {'large' } {'xlarge'}

Add the categories{'medium','large','xlarge'}toBafter the category'small'.

B = addcats(B,{'medium','large','xlarge'},'After','small'); categories(B)

ans =5x1 cell array{'xsmall'} {'small' } {'medium'} {'large' } {'xlarge'}

The categories ofAandBare now the same including their order.

Vertically concatenateAandB.

C = [A;B]

C =15x1 categorical arraymedium xlarge small small medium large medium large medium small small xsmall xsmall small small

The values fromBare appended to the values fromA.

List the categories ofC.

categories(C)

ans =5x1 cell array{'xsmall'} {'small' } {'medium'} {'large' } {'xlarge'}

Cis a 16-by-1 ordinal categorical array with five categories, such thatxsmall < small < medium < large < xlarge.

Related Examples

More About

Ordinal Categorical Arrays